Hackvertor and JSReg

Thursday, 11 March 2010

I’m not a developer any more so I find it difficult to update the experiments I’ve been working on but I managed today to upload the work I’ve done with JSReg and update Hackvertor. They are both integrated closely together because Hackvertor allows untrusted Javascript using JSReg.

The recent upgrade to JSReg allowed me to upload the Hackvertor changes I did a while ago, it is now very nice and easy to share code between users. At the moment registration is disabled but I plan to enable it once I’ve figured a way to stop user’s overloading the tag list.

You can see how the integrated JSReg parser works by visiting Public Hackvertor this will eventually replace the original one now online. There are only a limited set of tags as I’ve not had time to code them all but we have a couple of users on there that might start adding code if they haven’t forgotten their password =)

I found the untrusted Javascript feature difficult to code as sharing each tag inside a tag for example would require some tricky Javascript but I think I’ve managed to pull it off. I’ll document the JSReg stuff here and how Hackvertor allows tag objects inside tags.

Playing nice with JSReg

In order to use the parser effectively we need to be able to inject our own objects into the sandboxed environment without compromising the security of the sandbox. To do this JSReg supports some extension functions which allows you to inject a object directly. The following code sample shows you how to do it:-

So here the “parser” is the JSReg parser, we use the extendWindow function to place a “$tags$” object within the sandbox. Notice the $ prefix and suffix, this is how JSReg protects objects/properties. We use a closure to send a Hackvertor Tag object to the sandbox which passes it a function that accepts a tag object and a callback. Hackvertor now uses callbacks for each tag, this allows conversions to be run in sequence without waiting for each function to return the output.

A simplified version of this can be seen below, this time we assign a value from a dom object outside of the sandbox to a reference inside the sandbox.

parser.extendWindow('$code$',document.getElementById('input').value);

The new Hackvertor

All tags are now user definable! Each tag can have up to three parameters, provide some help text and call existing tags from inside the sandbox To create a tag you simply have to return some output, inside a tag it has some special variables that are automatically assigned when a tag is called. The special variables are listed below:-

code, params, tags

The code refers to the original text passed to your tag, this could be plaintext or some text that has been transformed by a previous tag. The params is a simple numeric indexed array which refers to any params supplied by the user so for instance if you tag supports 1 param, you can refer to it inside your tag as param[0]. Tags contains the Hackvertor tag reference mentioned previously and allows you to call existing tags without having to write the same code over and over. I will show below how you to call the base64 tag that currently exists in the Hackvertor tag space.

So this will call the tags function defined by extending the sandbox, it accepts a object and callback as it’s arguments. I send a string ‘abc’ and use the tag ‘base64′ I supply one param ‘encode’ and then use the callback to get the result of the conversion.